Another big way you get scooped up, having worked in that industry among other things - is that anybody - internal staff, customers, that one sales guy who insists on using his personal iPhone to demo the product and everybody turns a blind eye because he made $14M in sales last year - calls some public DNS resolver and the public DNS server sells those names --- even though the name didn't "work" because it wasn't public.

They don't sell who asked because that's a regulatory nightmare they don't want, but they sell the list of names because it's valuable.

You might buy this because you're a bad guy (reputable sellers won't sell to you but that's easy to circumvent), because you're a more-or-less legit outfit looking for problems you can sell back to the person who has the problem, or even just for market research. Yes, some customers who own example.com and are using ZQF brand HR software won't name the server zqf.example.com but a lot of them will and so you can measure that.